A scroll compressor is equipped with a paired fixed scroll and rotating scroll each having a spiral wrap provided upright on an end plate and is configured to compress fluid by causing a compression chamber, formed by engaging the scrolls, to move from its peripheral position toward the center while reducing in volume with the orbital rotary motion of the rotating scroll and to discharge the compressed fluid outwards through a discharge port provided at the central portion of the fixed scroll.
Such a scroll compressor is configured such that the compression chamber is reduced in volume while being sequentially moved to the center as the rotating scroll is rotationally driven and has a design volume ratio (compression ratio) defined by the ratio of the maximum volume of the compression chamber formed at the outermost peripheral positions of the scrolls when an intake is shut off to the minimum volume of the compression chamber directly before the engagement between the fixed scroll and the rotating scroll is released. A larger design volume ratio is efficient because it decreases the loss, and moreover, it is advantageous in terms of noise.
To increase the design volume ratio, normally, the technique of increasing the number of windings of the spiral wraps of the fixed scroll and the rotating scroll or the technique of using stepped scrolls in which the spiral wraps are high at the outer peripheral side and low at the inner peripheral side is used. In addition, as disclosed in PTLs 1 and 2, the technique of decreasing the minimum volume of the compression chamber as much as possible by decreasing the diameter of the discharge port, by forming the discharge port in an oval shape, or by forming the discharge port in a polygonal shape is sometimes employed.